The present invention relates to a roller formed of a sintered alloy having high wear resistance and assembled in a rotary compressor having high fluid tightness.
In a recent trend, a rotary compressor for use with domestic electrifications becomes light in weight and more compact in size. Further, for the reduction of production cost and for high performance of the compressor, improvements have been made on materials of respective mechanical components of the compressor.
A rotary compressor mainly includes, as shown in FIGS. 1 and 2, an outer case 10, a cylindrical housing 11 assembled in the case 10 and formed with a vane groove 11A extending in radial direction of the housing, a roller 13 rotatable eccentrically in the housing 11, a shaft 14 integrally fixed to the roller 13 for its rotation, and a vane 12 slidably disposed in a vane groove 11A and moved in radial direction of the roller 13. A compression spring 15 is disposed in the groove 11A to urge the vane 12 radially inwardly. Therefore, a radially inner end face of the vane 12 is in slide contact with an outer peripheral surface of the roller 13. A working chamber is provided by a space defined between the housing 11 and the roler 13, and the vane 12 devides the chamber into intake and discharge chambers. The intake chamber is connected to an intake port 16 and the discharge chamber is connected to a discharge port 17. A fluid sucked in the working chamber is compressed and fed out by the eccentric rotation of the roller 13.
Among those components, the vane 12 and roller 13 perform relative sliding motion at high load, and therefore, these components must have high wear resistance. On this standpoint, various materials, for example, sintered alloy, have been proposed for the materials of the vane and roller.
However, regarding the material of the vane, SKH51 has been still a major material in an actual production. SKH 51 is defined by JIS (Japanese Industrial Standard), which is a high-speed tool steel, containing 0.80 to 0.90% of C, 3.80 to 4.50% of Cr, 4.50 to 5.50% of Mo, 5.50 to 6.70% of W, 1.60 to 2.20% of V and balance Fe.
Further, regarding the material of the roller, a sintered material has been employed as described above rather than a cast iron. According to the proposed sintered material, a hard metal carbide and a metal oxide formed by a steam treatment are dispersed in a matrix. Such sintered alloy is disclosed in Japanese Patent Application Kokai Nos. 60-73082 and 60-174853.
More specifically, according to the publication No. 60-174853, it discloses a sintered alloy consisting of 3-10% by weight of chromium, 1-5% by weight of graphite and balance iron and impurities. Metal carbide, metal oxide and free graphite are dispersed in the tempered martensitic matrix. The metal oxide is formed at interiors of sintered voids by steam treatment. This metal oxide seals the sintered voids to thereby obtain lubrication oil retainability.
According to the publication No. 60-73082, it discloses a rotary compressor. A rotor and/or a vane are formed of ferrous sintered alloy. Metal carbide and metal oxide are formed during tempering and are dispersed in the tempered martensitic matrix. Further, nitrogen is solid-solved in the martensitic matrix.
The above sintered material for the roller is intended to improve wear resistance and fluid-tightness. The metal oxide which seals sintered pores serves to enhance fluid-tightness of the compressor. However, with the use of such sintered material, a compressor roller has been burdened with much higher load because of the recent use of an inverter system. Accordingly, such sintered material may be worn out and undergoes scuffing if applied in the inverter system. In order to overcome this problem, there is a further demand for further improvement on wear resistivity and scuffing by using specific composition instead of conventional metal carbide dispersed in the matrix.